Friday, October 26, 2012

Remarks on the purported distribution of Polyphylla mescalerensis Young
in Chihuahua, Mexico.

Based on a series of 19 males, Young (1988) described Polyphylla mescalerensis from the Mescalero Sand Dunes, of southeast New Mexico. The unknown female, at that time, was described in my subsequent paper of 1998:28.

Polyphylla mescalerensis Young
Topotype Male
Heretofore, the species has been thought to be restricted to this particular dune system and other contiguous pockets of sandy refugia.

Partial view of Mescalero Sand Dunes with summer monsoon approaching.

View of Mescalero Sand Dunes, sand blowouts in distance.

On pages 24 and 26 of Young's monograph, where two versions of his key to North American species are presented (one including male aedeagal characters, the other not), he cites "Chihuahua, Mexico" in the concluding dichotomy for P. mescalerensis.

Scarab Guru, Richard Cunningham

Curiously, however, he made no further explanation nor justification for the Chihuahuan citation any where in the publication. I suspect his addendum may have been a last minute addition to either his manuscript, or most likely, the galley proofs.

In the decades since Young's publication, no reference,
that I am aware of, to this alleged distributional extension
has been formally discussed or verified, apparently, being
overlooked by subsequent authors including myself.

Through a series of fortuitous events, aided by the generous assistance from fellow scarab enthusiast and guru, Richard Cunningham, I acquired a purported specimen of P. mescalerensis labeled as ...

 "MEX: CHIHUAHUA, Cerro San Luis, VIII-13-81, 1767m at light, Scott McCleve" 

and bearing a "R.M. Young 1988" determination label. Of course, I have no idea what or how many specimens Young examined to warrant the distributional amendment of P. mescalerensis. However, considering the coincidental year of his determination label, 1988 (below, right), and publication of his monograph,  also 1988, I would venture to speculate this is probably one of them.

  Polyphylla sp. male
Chihuahua, Mexico

Labels of Polyphylla specimen from Chihuahua, Mexico.
D.A. La Rue collection

In my paper of 1998:32, I invalidated Young's distribution of Polyphylla monahansensis Hardy & Andrews from, yet again, Chihuahua, Mexico. My reasoning was that a desert sand dune obligate would not also occur in a montane environment ("large canyon bottom," Young 1988:52; 5,000-5,500 ft.elevation, La Rue 1998:32). Sand dune obligates have evolved physiological, morphological, and behavioral adaptations allowing them to exist in such environments (La Rue 1998). In addition, most dune-inhabiting species of Scarabaeidae are apparently unable to survive in other desert areas (Hardy and Andrews 1987).  

Purported distribution of Polyphylla mescalerensis (sensu Young 1988).
With that being said, ...

It appears that similar circumstances prevail in the case at hand. Given the striking disparity of ecological parameters between the Mescalero Sand Dunes and Cerro San Luis (cerro, Spanish, meaning "hill"), a montane environment at 1767 meters (5800 feet) elevation, the Chihuahuan record for P. mescalerensis is here considered dubia notitia.

Consequently, the taxonomic status of the Cerro San Luis specimen, for which this post is based, comes into question.

Salient morphological characters (presence of pronotal and elytral setae; eroded, discontinuous elytral vittae; southwestern distribution) clearly indicate that it is related to P. diffracta Casey. Though the aedeagus of the specimen is in view, many authors, including myself, have noted significant intra-, and interspecific variation of this character thus regarding them of no diagnostic value. In addition, because of phenotypic variation often seen in any population of Polyphylla, definitive taxonomic assessment of the specimen cannot be made based solely upon one male exemplar ("T.L. Casey syndrome"). The possibility that it may represent an undescribed taxon is a valid consideration. However, a series of both sexes of adults is required to substantiate that possibility with any certainty.  

                                                 Literature Cited and Internet Resources

Hardy, A. R., and F. G. Andrews. 1978. Studies in the Coleoptera of western sand dunes. I. Five new Polyphylla Harris. Pan-Pacific Entomologist 54(1):1-8.

La Rue, D. A. 1998. Notes on Polyphylla Harris with a description of a new species. (Coleoptera:Scarabaeidae:Melolonthinae). Insecta Mundi 12(1/2):23-37. 

Young, R. M. 1988. A monograph of the genus Polyphylla Harris in America, North of Mexico. Bulletin of the University of Nebraska State Museum 11(2): vi+115 pp.

Map image courtesy of Google Earth.

                                            © Delbert La Rue 2010. All Rights Reserved.

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